Controlled induction heating with scanning



July 28, 1953 J, A. REDMOND 7,

CONTROLLED INDUCTION HEATING WITH SCANNING Filed May 14, 1949 Fig.2 Fig. l.

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WITNESSES: I INVENTOR .John A. Redmond.

7 BY 722v- ATTORNEY Patented July 28, 1953 UNITED STATES OFFICE CONTROLLED INDUCTION HEATING WITIE' SCANNING John A. Redmond, Baltimore, Md.,, assignor to Westinghouse Electric, CorporatiomEast Pitts.- burgh,,Pa., a corporation of Pennsylvania Application May 14, 1949, Serial- No. 9352 76 6 Claims. 1,

My invention relates to the induction heat.- ing of Work or work-pieces by highrfrequency power derived from a: high-frequency generator. It seeks to provide an improved, inexpensive, and exceedingly simple means, comprising. a workreceiving coil-portion and a separate power-com trol coil-portion, which is utilizable for? controlling the loading on the high-frequency generator, and for controlling, in any desired way, thepower delivered to the work, and for other purposes.

The power that a high-frequency power-supply system will deliver to an inductioivheating or work-receiving coil is materially influenced by the inductance of the circuit which includes the coil. For a given work-application, the inductance of the induction-heating or workrecciv ing coil is predetermined by the nature of the work therein. In accordance with my invention'the high-frequency generator supplies highfrequency current to a branch circuit that includes a variable power-control coil in addition to the work-receiving coil. The power-control coil is physically and magnetically separate from the work-receiving coil, and is used to adjust the inductance of the branch-circuit for improving the iiexibility of the induction-heating system of which it is a part.

In accordance with a preferred form of my invention, the branch-circuit isa unitary piece of equipment that includes the power-control coil and the work-receiving coil; and consequently, the equipment can also be designated as an induction-heating coil-means. The total inductance of the branch-circuit (or the induction-heating coil means oi the preferred embodiment) is made up of the inductances of both the work-receiving and the power-control coils; and the total inductance is adjusted, either manually or automatically, through the power-control coil; By having the power-control coil compensate for changes desired for, or taking place in, the Work-receiving coil, the induction-heating system can have a Wide range of application for heat-treating different types of work, or heat" treating'a single work-piece in diiierent ways.

I accomplish the foregoing control by variably inserting a metallic bar into and out of the magnetic field of" the power-control coil; Preferably the-bar is'apiece of copper, aluminum, silver,

or other highly conductive metal; For want of a better name, I call such a piece of metal, a slug. The slug can be of simple shape or of a more: complex shape, and, if" desired, can be cooled 'in any suitable way. A simple design for the slug is usefuliprimarily in manually adjustable applications of theinvention. A more-complex design, has more utility in connection: with scanning operations in which a long piece of metal is heated by scanning it: with a short work receiving coil; The slug and work are simultaneously scanned; the former by the powercontrol coil and the latter by thework receiving coil. A- varying, shape of. the slug will change the power to the work-receiving; coil for variably heating different portionsof the'work being scanned; or for varying theinductance of the induction-heating coil means in, accordance. with work of special shape.

Objects, features. and innovations in addition tothe foregoing will be discerniblefr-om; the following; description of preferred embodiments of: my invention. The descriptionis to be taken in conjunction with the simplified and somewhat schematic drawing attached hereto, In the drawing; which is not. to; scale:

Figure. l isa simplified. View of: an inductionheating systemin accordance with my invention, the branch-circuit equipment or induction-heating coil-means being shown in plan and. parts therein in section;

Figure 2 is a sectional view substantially on the lines I1---II of Fig. l;

FigureBis a plan'view of an induction-heating coil-means in accordance-with my'invention', but without cooling means;

Figure 4 is a partial" perspective view of an automatically-operating scanning embodiment of my invention;

Figure 5 is a sectional View for illustrating a further embodiment of my invention; and

Figure dis a vertical view of still another modifled formof slug.

Figures 1 to 3 show a manually controllable embodiment of my invention. A high-frequency generator Z'delivers power for an induction-heat"- ing coil-means lthrough acurrent transformer 6' having a primary winding 8 and a secondary winding I 0. Thegenerator 2' is of the tube-oscillator type capable of delivering high-frequency power'usuallyat above 100,000 cycles per second; and the primary winding 8 may form a minor portion of the inductance of the tank circuit of the tube-oscillation generator- 2'. I desire it to be understood, however, that the highfrequency power may be supplied to the induction-heatingcoil-means 4' through any suitable meansincluding; for example, an impedancematching or a power-factor correcting: network.

The induction-heating coil-means 4:. comprises a strap-conductor unit of solid metal, fabricated shaped as shown, for carrying the high currents usually necessary for induction heating. The unit comprises a work-receiving coil i2 and a round inductance-varying or power-control coil id. Each of the coils l2 and I4 is flat and substantially a complete turn with a slight space between its ends for insulation. The unit 4 further comprises a straight strap-conductor [5 connecting a first end of the work-receiving coil l2 with a first end of the power-control coil M; and a pair of relatively insulated straight strapconductors I8 and having ends connected to the other ends of the coils. In the embodiment disclosed, the conductor I6 is substantially in line with the conductor l8, both of which are parallel to and spaced from the conductor 20; and the other ends of the conductors l8 and 20 are connected to relatively insulated lugs 22 and 2d. Conductors 26 and 28 connect the lugs 22 and 24 to turns of the secondary winding l0.

Tubing 3c is secured, with good thermal contact, to the outside of the straps which form the various conductors and coils, and hence the tubing 39 can be considered part of the unit. The tubing 30 is connected to insulating hoses 3% through which water or other cooling liquid is fed to and taken from the tubing.

The secondary winding I0 provides a highfrequency voltage across the lugs 22 and 24, so that high-frequency power is delivered to the branch-circuit or induction-heating coil-means 4. Hi h-frequency current will flow through the work-receiving coil i2 for heating a piece of work W therein. For controlling the inductance of the branch-circuit, a piece of metal, or slug, 32 is insertable to different extents in the power-control coil i l and is adjustably carried by a fixed support 35.

The slug 32 has a cylindrical portion 35 and a tapered portion 38. Preferably, the outer diameter of the portion 3 .3 is less than the inner diameter of the power-control coil M. A handle extends from the cylindrical portion 36 and passes through a set-screw means 42 in the support 34 so that the position of the slug 32 with respect to the power-control coil M can be varied. The slug 32 is coaxial with the power-control coil l4, and the tapered portion 38 is preferably longer than the axial length of the power-control coil 14. The closest coupling between the coil l4 and the slug 32 is obtained when the cylindrical portion 3% of the slug 32 is full immersed in the coil M. Obviously, looser coupling is obtained by raising the slug so that the tapered portion 38 lies in the coil l4.

Preferably, the slug is of copper which i comparatively low in cost and high in conductivity. However, any other highly-conductive metal member, which will absorb little electrical energy while significantly aifecting the magnitude of the inductance of the branch-circuit, can be used. Aluminum and silver, for example, are satisfactory. The transverse diameter of the slug is made less than the inner diameter of the powercontrol coil It so that the slug will not physically contact the coil in any of its operating positions. An advantage of using a taper on the slug lies in the fact that the taper can be made to any desired angle for determining the sensitivity of the variations in inductance provided by the adjustment of the slug 32 in the power-control coil l4.

Preferably, the slug is water cooled. To this end, it is made hollow. When the slug is small is diameter, insulating hoses can be directly connected to its ends. When the slug is large in diameter, metal tubing 44 can be helically or otherwise secured inside of it for receiving cooling liquid in any suitable manner. This is the embodiment shown in Fig. 2.

The operation of the apparatus thus far described is believed to be clear to anyone skilled in the art. The work-receiving coil l2 and the power-control. coil H are electrically in series. Consequently, the reactance of the branch-circuit consisting of the induction-heating coil-means 4 comprises the summation of the reactance of the two coils I2 and i4 and the strap-conductors l6. l8 and 26 in the branch-circuit. Work W placed in the work-receiving coil i2 affects the inductance of the circuit, but the change in inductance can be compensated for by adjusting the slug 32 in the power-control coil 14. Moreover, the slu 32 can be adjusted differently for different workpieces in the work-receiving coil l2. Such apparatus lends itself to several uses. The slug can be adjusted for the purpose of providing a substantially constant current-flow through the work-receiving coil, or for the purpose of changing the power delivered into the work in the workreceiving coil, or for the purpose of balancing or matching the reactance of the induction-heating coil-means to the electrical network or circuit to w .ich it is connected.

An embodiment of my invention which seems to me at present to be more important than that heretofore described is shown in Fig. 4. This embodiment illustrates, in a simplified fashion, apparatus for automatic scanning work, such as for example, an elongated steel rod or bar. The rod or bar is moved relatively with respect to the work-receiving induction-heating coil. The figure illustrates apparatus in which a movable bar or rod is passed through a stationary work-receiving coil; but it is apparent that the scanning operation can be reversed and the coil progressively moved over a stationary rod or bar.

Referring to Fig. 4, any suitable movable scanning device is represented by the reference numeral 56. The device 58 comprises a movable frame-bar 52 carried in any suitable stationary guides 54 for rectilinear movement. The scanning device 56 is moved between proper limits by any suitable means, herein shown as comprising a rack 56 on the frame-bar 52, and a gear 58 which meshes with the rack. Preferably, the gear is reversibly driven by an electric motor and gearing.

Spaced arms 60 and G2 are secured to the framebar 52 and removably hold a work-piece and a slug. The arm 69 comprises a main section 64 hinged to frame-bar 52, and an outer section 66 hinged to the main section. The sections are force-biased to horizontal position. The main section 34 adjustably carries a centering pin 68; and the outer section 65 adjustably carries a centering pin 70. The arm 62 is fixed to the framebar 52 and is provided with holes and set-screw means 12 and i4 over the holes. The holes are in line with the pins 58 and 19 and adjustably receive much longer centering pins 73 and 15.

The aligned pins 68 and 16 removably carry a slug 8B; and the aligned pins Ill and I8 removably carry a work-piece 82. The outer section 66 of the arm 6!) can be separately raised for replacing work-pieces without disturbing the slug 80. When it is desired to change a slug, the main section M of the arm is raised.

An induction-heating coil-means 4 is supported in any suitable manner between the arms scanning (device is movable, "the coil-means 4 is supported "so as to be Stationary with a espect thereto. The Work-receiving coil 1-2 or the induction-heating coil-means 4 a common axis with the workpins l and 118 and the workpiece 82; and the axis of the power-control coil 14 corresponds to that of the slug-pins 68 "and 16 and the slug' 8ll.

The slug '8!) is shown as of cylindrical shape; that is, itsgeneratrix lines -':are all parallel and pass througl-i a -oircle having its :center in the axis of the-13111568 and '15 'and power-c'ontrol e'oil ll.

Assume that the outer surface of the work "82, =-which "is a-cylindrical shailt, is to :be 'n'iildly'heated for a length or distance between the imaginary 'lines A and B, and that the remaining portion of the shaft between the imaginary lines Band "C is to'b'e'heated-more intensely. "The-centering pins 1-6 andl'S 'area'diiusteduntil line B is -in"the pianeof the bottomen'd of theslug to. Assume also that "at the start or the heating operation, the lower arm 52 of the scanning device '50 is "close to the "bottom of the induction-heating coil- T means 4 so that the bottom of the shaft 82 is just above the top of the worli receiving coil 1 2.

For the heating operation, the indudtion heating coil-means 4 is energized and the scanning device 50 is permitted to drop, preferably at a constantspeed. Asth'e'scannin'g device 50 drops, the lower "end-of the shaft 82 entersthe work-receiving coil Hand is inductively heated. As the scanning device 5%!continues to drop, the shaftportion inside the coil I2 is heated so'thatthe J.

shaft 'is progressively lre'ate'd at a predetermined relatively mild rate, until the line B is reached.-

ture moves down to its lower'l'imit of movement.

.An advantage of the invention resides "in the 'fact that the inductance in the induction-heating coil-means 4 can be varied without the use of sliding or rolling contacts. -Moreover, the power-control coil and slug give sensitive control in the 'lowinductance .range usually iound Lin induction-heating Work-receiving coils of a typehaving one or a few turns. Obviously, both the work-receiving coil and the power-control coil can be made of more than one turn if desired;

The length, shape and other physical characteristics of the slugs can be varied to suit individual heating applications. In Fig. 4, the slug 8D is shown as a solid cylinder having a regular outer surface with an axial length equal to the length B-C along the shaft 82 simply because this length of the shaft is to be heated hotter than the rest of the shaft. However, the slug can he irregularly shaped and sized differently depending on the heating pattern to be applied to the particular work-pieces to be heated.

An example of such a variation is shown in Fig. 5 which can be considered to be a section of an induction heating means such as shown in Fig. 3, with the section taken in a plane which includes the axes of a work-receiving coil 90 and a power-control coil 92, it being understood that these two coils are electrically connected .in a single branch-circuit fed from a common source of high-frequency power. The respective coils scan a workpiece :94 and :a solid slug :96. In this particular' embo'diment, the work-piece and :slug are fof the same axial length, both being considerably longer than the axiallength of the respective coils. It will be observed that the :gen'eratrices or the surface of the slug 96 are .not-parallel straight lines. Eachli-ne has a convex outward portion at the-central part of the slug.

As the work-piece is scanned from end to end, the narrower end portions of the slug -96 are more loosely coupled to the power-control "coil thanthe central bulged portion of the slug. As a result, the central part of the work-piece 94 will 'be heated. more intensely than its end portions. If the scanning is done at a constant 7 speed, harder surfaces can be provided at such central portions 'of the "work-piece, assuming that *a' quench' -coil is suitably associated with the Work- 'recei-ving coil 90.

Frequently, irregular parts having sharp ends, slots, hollow portions, etc, must be inductively heat-treated without overheating of the sharp edges oisuchendsyslots, etc. For'such'heating, copper slugs can be provided which are relatively more closely coupled to the power-control coil except when such ends, slots, etc., are being scanned by'the work-receiving 'coil. During such times, theslugcanspresenta slot or other-surface which lowers its coupling to the power-"control coil and thereby lowers the power supplied to the *work rec'eiving co'ilit being assumed that maximum power transfer to the work is accom panied by maximum coupling between the slug and the power-control coil. The shape of the slug 'canbe suitably found "by trial anderror or "can even be calculated. Figure 6 illustrates a slug for such application. The slug 100 has an upper concave'inward portion l02n'earits "top and a slotted portion I04 somewhat "below the concave portion I02.

While I have-described m invention inseveral different embodiments, it is obvious that its "principles have wide application, especially for automatic scanning. Its principles, therefore, canfind themselves embodied in many different modifications and'embodiments'other than those "herein described by way of illustration as forms at present preferred.

I claimas my invention:

1. An induction-heating system for an elongated workpiece comprising, in combination, a high-frequency transformer having a primary winding adapted to be supplied with high-frequency energy and a secondary winding, an

induction-heating coil-means comprising a pair of relatively-insulated conductors to which highfrequency energy is supplied by said secondary winding, a power-control coil comprising at least one turn having an axis, a work-receiving coil comprising at least one turn having an axis, said axes being parallel, one of said conductors being connected to an end of said power-control coil, and the other of said conductors being connected to an end of said Work-receiving coil, a conductor connecting the other ends of said coils, a slug having a portion insertable into and removable out of said power-control coil without contact therewith, and supporting means for said slug enabling said slug-portion to be fixed in position relative to said workpiece and to be moved relatively with respect to said power-control coil so as to be either fully inside or fully outside of said power-control coil.

2. An induction-heating coil-means comprising a pair of separate coils, each comprising at least one turn; a conductor extending from an end of a first coil to an end of the second coil; relatively insulated conductors extending from the other ends of said coils; said first coil being an induction-heating coil adapted to receive Work to be inductively heated; a piece of conductive metal; said second coil being adapted to receive a portion of said piece of metal axially therein; said portion having an outer surface which is diametricallysmaller than the inside of said second coil so that it does not touch said second coil; work-supporting means comprising a scanner operable for scanning work with said induction-heating coil; and means for supportin gsaid piece of metal in a predetermined position relationship to said work so that its said portion is movable to different extents in said second coil when said scanner is operating to scan said Work.

3. An induction-heating coil-means for heating a piece of work, comprising a pair of separate coils, each comprising at least one turn; a conductor extending from an end of a first coil to an end of the second coil; relatively insulated conductors extending from the other ends of said coils; said first coil being an induction-heating coil adapted to receive a piece of work to be inductively heated; a piece of metal; said second coil being adapted to receive a portion of said piece of metal axially therein; said portion being diametrically smaller than said second coil so that it does not touch said second coil; said portion having an outer surface which is other than a continuous surface generated by parallel straight line generatrices; and supporting means having supporting means for supporting said piece of metal and piece of work; said supporting means being relatively movable with respect to said coils, for relatively moving said piece of metal and work with respect to the associated coils.

4. An induction-heating coil-means for heating a piece of work, comprising a pair of separate coils, each comprising at least one turn; a conductor extending from an end of a first coil to an end of the second coil; relatively insulated conductors extending from the other ends of said coils; said first coil being an induction-heating coil adapted to receive a piece of work to be inductively heated; a piece of metal; said second coil being adapted to receive a portion of said piece of metal axially therein; said portion being 8 diametrically smaller than said second coil so that it does not touch said second coil; said portion having an outer surface which is other than a continuous surface generated by parallel straight line generatrices; and supporting means having supporting means for supporting said piece of metal and piece of work; said supporting means being relatively movable with respect to said coils, for relatively moving said piece of metal and work with respect to the associated coils, said work-supporting means providing a work-receiving space of sufiicient length to support a piece of work which is axially longer than said first coil, and said portion of said piece of metal being axially longer than said second coil.

5. An invention including that of claim 4, but further characterized by said portion of metal being axially shorter than said work-receiving space.

6. An induction-heating system comprising, in combination a pair of separate coils, each comprising at least one turn, and conductor means connecting said coils in a common branch circuit for receiving energy from a single source of power, a first of said coils being an inductionheating coil adapted to receive work to be inductively heated, the second of said coils being adapted to receive a coupling-varying member that can be variable coupled to said second coil for changing its effective inductance, scanner means comprising a movable support associated with said work and induction-heating coil for relatively scanning the work with said inductionheating coil, and a movable support mechanically interconnecting said scanner means and said coupling-varying member for relatively scanning said coupling-varying member with said second coil in conjunction with the operation of said work-supporting scanner means.

JOHN A. REDMOND.

References Cited in the file of this patent UNITED STATES PATENTS 

